1. Field of the Invention
The disclosure of the present invention relates to an inkjet recording liquid and an inkjet recording device using the liquid, and relates especially to satisfactory intermittent discharge properties and bronzing suppression.
2. Description of the Related Art
In general, inkjet recording devices form an image on a recording medium by discharging a recording liquid from a recording head onto the recording medium as the recording medium is being transported. Due to rapid advances in inkjet recording technology in recent years, it is now possible to obtain high-definition images equivalent to silver halide photographs when using photographic paper as the recording medium.
However, because in recording with such inkjet recording devices the recording head forms an image without making contact with the recording medium, the image may be corrupted by satellite behavior, in which droplets of the recording liquid are displaced in the transport direction of the recording paper. One cause of the satellite behavior is increased viscosity of the recording liquid as it dries in the nozzle of the inkjet recording device.
In the case of intermittent printing, when there are long intervals between printing the discharge properties of the recording liquid (hereunder called intermittent discharge properties) show a tendency towards increased viscosity of the recording liquid in the nozzle because the recording liquid is more likely to dry in the nozzle the longer the discharge interval. In low-temperature environments in particular, the change in viscosity is greater relative to the drying rate, so that the viscosity of the recording liquid increases rapidly even if there is a slight rise in the drying rate, and satellite behavior is much more likely to occur.
Satellite behavior can be suppressed by increasing the surface tension of the discharged recording liquid to make the droplets more cohesive. The surface tension of the recording liquid can be increased by ensuring that there is no unattached pigment dispersion resin in the recording liquid, but when there is no unattached pigment dispersion resin, bronzing is more likely to occur.
For example, it has been reported that in an ink composition for inkjet recording containing a pigment dispersion including a dispersed water-soluble styrene-(meth)acrylate resin, good recorded images and stable discharge from the inkjet recording head can be obtained by setting the content of the water-soluble resin and the content of the unattached water-soluble resin within specific ranges. However, although this ink composition is superior in terms of stable discharge, there has been no research into strategies for dealing with the problems of bronzing and deterioration of the discharge properties during intermittent printing with long intervals between ink discharge, especially in low-temperature, low-humidity environments.
It has also been reported that with an aqueous ink having a pigment contained in non-water-soluble polymer particles, images with superior image clarity and printing concentration can be obtained by keeping the average particle diameter of the polymer particles, the content of unattached polymer and the pigment content within specific ranges. However, since this aqueous ink uses water-insoluble polymer particles with a small average particle diameter, the viscosity of the ink is likely to change due to re-aggregation of the polymer particles in low-temperature, low-humidity environments, so there is room for improvement in the intermittent discharge properties of the ink.